I think the "casting" says more about Cruise's somewhat confused perception of himself than it does about anything else !
Or do I mean over-inflated ego and...ditto... ?

Yes, that's the one.

He clearly sees nothing strange about trying to play a very large, charismatic one-man army - it would take a very good small actor indeed to pull off such a stunt, and that he ain't, victuaria has it right I think. Mind you, he may have money in the project don't forget, which could skew the whole situation.
Actually, I think Richard Grere would be better, certainly in the acting stakes - but still not the biz, and too old, as is Cruise.

Course, Polyfilla shares will go up ..............

Perhaps Cruise simply hasn't read the books - which doesn't exactly say a lot for what the scriptwriters have come up with to "tempt" him.